Method of wavelet coding a mesh object

ABSTRACT

The invention relates to a method for the encoding of an object with at least two dimensions, that is associated with a basic mesh consisting of a set of basic facets, and with coefficients in a base of wavelets corresponding to local modifications in said basic mesh, said method delivering a total data stream that can be used to reconstruct said object.  
     According to the invention, said wavelet coefficients are partitioned into at least two separated subsets each undergoing an independent encoding, and said method inserts positioning data in said total data stream, enabling the identification of wavelet coefficients relative to a portion of said object in said total data stream, so as to enable a selective reconstruction of said portion by means of the coefficients of at least one of said subsets.  
     The invention relates to a method of coding an object having at least two dimensions which is associated with a basic mesh comprising a set of basic surfaces and with coefficients in a base of wavelets corresponding to local modifications to said basic mesh. The inventive method delivers a global data flow that can be used to reconstruct the object. According to the invention, said wavelet coefficients are partitioned into at least two disjoint subsets each of which is encoded independently. Subsequently, positional data are inserted by the method into the global data flow which can be used to locate wavelet coefficients relative to a portion of the object in said global data flow, in such a way as to enable a selective reconstruction of said portion using the coefficients of at least one of said subsets.

[0001] The field of the invention is that of the encoding of meshedobjects with at least two dimensions. More specifically, the inventionrelates to the representation and encoding of meshes, or ofmeshed-encoded textures, associated with objects of a graphic sceneimplementing a method known as a “wavelet” method. The invention can beapplied more particularly but not exclusively to second-generationwavelets, presented for example in Wim Sweldens, “The Lifting Scheme: AConstruction of Second Generation Wavelets”, SIAM Journal onMathematical Analysis, Volume 29, number 2, pp 511-546, 1998.

[0002] The invention can be applied in all fields where it is desirableto optimize the storage and/or the transmission of images. The inventioncan be applied especially but not exclusively to the, storage andtransmission of 3D models, lifting grids, and objects and texturesencoded by two-dimensional meshes.

[0003] It may be recalled that what are called “wavelet” encodingmethods are used to represent a mesh as a succession of details added toa basic mesh. The general theory of this technique is describedespecially in M. Lounsbery, T. DeRose and J. Warren, “MultiresolutionAnalysis for Surfaces of Arbitrary Topological Type” (ACM Transactionson Graphics, Vol. 16, No. 1, pp. 34-73, January 1997).

[0004] The general principle of this technique consists in developinghomeomorphism between an object to be encoded (such as a 3D mesh forexample) and a simple mesh (more generally called a “basic mesh”) in abase of particular functions, called second-generation wavelets.

[0005] In this technique, a mesh is therefore represented by a sequenceof coefficients that correspond to the coordinates, in a base ofwavelets, of a parametrization of said mesh by a simple polyhedron.

[0006] An object encoded according to such a technique thus takes theform of the union of the following two elements:

[0007] the basic mesh, which generally has few facets, and represents acoarse version of the object to be encoded;

[0008] the wavelet coefficients, which are triplets of real numbersassigned simultaneously to a precise zone of a basic mesh and to a givenlevel of subdivision of this mesh. These wavelet coefficients representthe refinements to be made to the zone with which they are associated inorder to converge towards the geometry of the initial object.

[0009] To enable the reconstruction of the representation of the encodedobject on the display terminal, it is necessary to send this displayterminal, firstly the basic mesh and, secondly, the associated waveletcoefficients. To this end, a method has to be defined for the efficientencoding of the wavelet coefficients, in order to compress and transmitthem, for example by means of communications networks, to the displayterminal which may be a remote terminal.

[0010] Up till now, it is the encoding technique known as the“zero-trees” encoding technique that gives the best results in terms ofcompression of the wavelet coefficients to be transmitted. Such atechnique consists in describing an order of encoding of the waveletcoefficients. This order is predetermined and known in advance to thesender and receiver terminals (for example a server and a customerdisplay terminal). Such a technique therefore makes it possible, duringthe transmission of wavelet coefficients, to avoid transmittinginformation on the ranges of coefficients that are not significant forthe encoding of the object considered.

[0011] Such “zero-trees” encoding operations are generally coupled witha “bit-plane” encoding operation which makes it possible, during thetransmission of the coefficients, to first transmit the most significantbits of each coefficient.

[0012] A more detailed description of the “zero-trees” technique will befound in Jerome M. Shapiro, “Embedded Image Coding Using Zerotrees ofWavelet Coefficients” (IEEE Trans. Sig. Proc. 41(12), December 1993) andA. Said, W. A. Pearlman, “A New, Fast, and Efficient Image Codec Basedon Set Partitioning in Hierarchical Trees” (IEEE Trans. Circ. System.For Video Tech., 6(3), June 1996).

[0013] These techniques, initially developed for the encoding oftwo-dimensional images, have recently been applied to second-generationwavelet coefficients as described in A. Khodakovsky, P. Schroder and W.Sweldens, “Progressive Geometry Compression” (SIGGRAPH 2000 proceedings)and F. Moran and N. Garcia, “Hierarchical Coding of 3D Models withSubdivision Surfaces” (IEEE ICIP 2000 Proceedings).

[0014] In the last two references cited, the encoding technique relieson the arbitrary adoption pf a hierarchy between the coefficients ofwavelets to be transmitted, making it possible to determine their orderof transmission to a remote display or storage terminal. This order,which is known to the receiver terminal, enables it to reconstruct theentire object transmitted.

[0015] One drawback of these prior art techniques is that the server incharge of the transmission of the wavelet coefficients to a displayterminal cannot select the coefficients that it wishes to send, andtherefore systematically transmits all the coefficients to the customerterminal.

[0016] Now, it often happens that the customer needs to receive only therefinements associated with a portion of the basic mesh. For example,when making a virtual visit of a museum, a customer may initially wishto look at an overall view of the sculpture and then at only a detail ofthe face. All that he needs therefore are the wavelet coefficientscorresponding to the refinements of the basic mesh on this portion ofthe face.

[0017] With the use of the prior art techniques, it is impossible forthe server to pick out the unnecessary coefficients and send only theencoding portion corresponding to the zone that the customer wishes toview.

[0018] One drawback of these prior art techniques therefore is that thecustomer receives all the wavelet coefficients, including thosecorresponding to the encoding of the portions of the object that he doesnot wish to view and does not need.

[0019] The communications network used for the transmission of thewavelet coefficients is therefore unnecessarily burdened, and the bitrate of transmission of the payload coefficients drops accordingly.

[0020] Furthermore, if the display terminal has low processingcapacities, then the reconstruction of a view of the object using allthe wavelet coefficients becomes a lengthy process, and this isdisagreeable to the customer.

[0021] Another drawback of these prior art techniques therefore is thatif the customer wishes to carry out an adaptive decoding so as todisplay only those portions of the object that are valuable to him, thenhe must himself sort out the wavelet coefficients transmitted. Thecustomer must therefore decode the entire data stream transmitted by theserver or coming from a data carrier, and then judge the relevance ofthe wavelet coefficients thus decoded as a function of the portion ofthe mesh with which they are associated.

[0022] As a consequence, one drawback of these prior art techniques isthat, to carry out adaptive decoding, the customer must have a displayterminal available with sufficient processing capacities to carry outthe operations of decoding the total stream, selecting the relevantcoefficients and reconstructing a representation of the object from thecoefficients thus selected.

[0023] In other words, one drawback of these prior art techniques isthat it is impossible for a customer having a display terminal withlimited processing capacities to carry out adaptive decoding.

[0024] It is a goal of the invention especially to overcome thesedrawbacks of the prior art.

[0025] More specifically, it is a goal of the invention to implement atechnique for the encoding of an object by wavelets, enabling a displayterminal to carry out the decoding of the object.

[0026] Another goal of the invention is to provide a technique for thewavelet encoding of an object, enabling a server to select certainwavelet coefficients, and transmit the selected coefficients as afunction of a zone of the basic mesh with which they are associated. Inparticular, it is a goal of the invention to enable a server to transmitonly certain wavelet coefficients, as a function of a customer'srequest.

[0027] It is yet another goal of the invention to implement a techniquefor the encoding of meshes representing 3D objects or scenes, thetechnique enabling an adaptive reconstruction of a mesh within a displayterminal.

[0028] It is another goal of the invention to provide a technique forthe wavelet encoding of an object, the technique being adapted todisplay terminals having low processing capacities.

[0029] It is yet another goal of the invention, naturally, to provide atechnique for the reconstruction and transmission, through acommunications network, of an object encoded according to this encodingmethod. In particular, during a transmission of this kind, it is a goalof the invention not to unnecessarily burden the communicationsnetworks.

[0030] It is yet another goal of the invention to implement a techniquefor the wavelet encoding of an object that is adapted to transmissionthrough a communications network with low bit rate.

[0031] These goals, as well as others that shall appear here below, areachieved by means of a method for the encoding of an object with atleast two dimensions, that is associated with a basic mesh consisting ofa set of basic facets, and with coefficients in a base of waveletscorresponding to local modifications in said basic mesh, said methoddelivering a total data stream that can be used to reconstruct saidobject.

[0032] According to the invention, said wavelet coefficients arepartitioned into at least two separated subsets each undergoing anindependent encoding, and said method inserts positioning data in saidtotal data stream, enabling the identification of wavelet coefficientsrelative to a portion of said object in said total data stream, so as toenable a selective reconstruction of said portion by means of thecoefficients of at least one of said subsets.

[0033] Thus, the invention is based on an entirely novel and inventiveapproach to the wavelet encoding of an object and to the shaping of thedata thus encoded within a total data stream.

[0034] Indeed, the invention relies especially on the generation of atotal data stream within which the wavelet coefficients can easily beidentified as a function of the portion of the meshed object with whichthey are associated. This is made possible especially, in the context ofthe invention, by the insertion of the positioning data within the datastream so as to enable an adaptive display of the encoding object by acustomer terminal.

[0035] Advantageously, each of said separated subsets is a basic facet.

[0036] It is thus easy, within the total data stream, to identify thewavelet coefficients associated with each of the basic facets throughthe presence, in the stream, of positioning data. It is thus possible toselectively reconstruct a portion of a meshed object, from waveletcoefficients associated with the facet or facets of the portionconsidered.

[0037] Preferably, said encoding implements the following steps:

[0038] the detection of at least one non-significant part;

[0039] the specific processing of each of said non-significant parts.

[0040] Indeed, an encoding of the subset of wavelet coefficients (namelya conversion of these coefficients into a binary sequence) takingaccount of the non-significant parts makes it possible to achieve abetter compression rate of these coefficients with a view to theirtransmission.

[0041] Preferably, said encoding implements a “zero-tree” type oftechnique.

[0042] Indeed, to date, the “zero-tree” technique is the one that givesthe best compression results. It is of course also possible to envisagethe use of any other technique for the encoding of wavelet coefficientswithin the total data stream, adapted to the implementation of theinvention.

[0043] According to a first variant of the invention, said total datastream comprises a header, comprising at least certain of saidpositioning data, and a wavelet coefficient zone, comprising a sub-zoneidentified by said positioning data for each of said separated subsets.

[0044] Thus, if the list of the wavelet coefficients has beenpartitioned into N subsets, each corresponding to a portion of themeshed object, the zone of wavelet coefficients of the total data streamcomprises N sub-zones, identifiable within the stream, by means of thepositioning data.

[0045] It will be noted here that the positioning data enabling theidentification of a sub-zone of the stream may be included in the headerand/or in any other part of the data stream.

[0046] Advantageously, said positioning data contained in said headeridentify a sub-zone, in defining a distance between the position of anidentified element and the starting point of said sub-zone in saidstream.

[0047] An identified element of this kind may be, for example, thestarting point or the end of the header, or any other element whoseposition in the stream can easily be known. The distance may beexpressed, for example, in numbers of bits.

[0048] Advantageously, said header furthermore comprises at leastcertain pieces of the information belonging to the group comprising:

[0049] the number of basic facets;

[0050] the type of wavelets;

[0051] information on said object;

[0052] information on the encoding of said positioning data.

[0053] This information can be exploited by a display terminal for thereconstruction, from the stream, of a representation of a portion or ofthe totality of the meshed object.

[0054] According to a second variant of the invention, said total datastream comprises at least one zone of wavelet coefficients, comprising asub-zone identified by said positioning data for each of said separatedsubsets, said positioning data comprising at least one marker at thestarting point and/or at the end of each of the sub-zones.

[0055] Thus, the positioning data are distributed throughout the totaldata stream, and are not grouped together in a header, as was the casepreviously.

[0056] Preferably, said sub-zones are organized in said stream by risingorder of basic facet.

[0057] Thus, when each of the basic facets undergoes an independentencoding (for example of the “zero-tree” type) it is provided that thesub-zones will be arranged within the stream as a function of theordinal number of the basic facet with which they are associated, forexample in rising order.

[0058] The invention also relates to a method for the transmission of adata stream between, firstly, at least one server and/or at least onedata carrier and, secondly, at least one display terminal, said datastream enabling the reconstruction of an object associated firstly witha basic mesh constituted by a set of basic facets and, secondly,coefficients in a wavelet base corresponding to local modifications insaid basic mesh.

[0059] According to the invention, a method of transmission of this kindcomprises:

[0060] a step for the reception of a request defining a portion of saidobject to be viewed;

[0061] a step for the analysis of positioning data present in saidstream, as a function of said request, making it possible to identifywavelet coefficients relative to said portion in said data stream;

[0062] a step for the extraction of said identified wavelet coefficientsto form a reduced data stream;

[0063] a step for the transmission of said reduced data stream.

[0064] Thus, a server, upon the reception of a request from a customeron a portion of the object, may make a selection, within the total datastream, of the subset or subsets of coefficients associated with theportion of the object considered. It can then construct a reducedstream, from the coefficients of the subset or subsets concerned, andtransmit it to the customer's display terminal.

[0065] The invention also relates to a signal representing an objectassociated with a basic mesh consisting of a set of basic facets, andwith coefficients in a base of wavelets corresponding to localmodifications in said basic mesh, comprising at least one zone ofwavelet coefficients and at least one positioning zone, comprisingpositioning data enabling the identification of the wavelet coefficientspertaining to a portion of said object and said signal.

[0066] According to a first embodiment of the invention, said waveletcoefficients being partitioned into at least two separated subsets eachundergoing an independent encoding operation, a signal of this kindcomprises a header comprising at least certain of said positioning data,and a zone of wavelet coefficients, comprising a sub-zone identified bysaid positioning data for each of said subsets.

[0067] According to a second embodiment of the invention, said waveletcoefficients being partitioned into at least two separated subsets eachundergoing an independent encoding, a signal of this kind comprises atleast one zone of wavelet coefficients, comprising a sub-zone identifiedby said positioning data for each of said subsets, said positioning datacomprising at least one marker at the starting point and/or at the endof each of the sub-zones.

[0068] The invention also relates to a data carrier designed for thestorage of at least one object encoded according to the method describedhere above.

[0069] The invention also relates to a system for the transmission of adata stream between, firstly, at least one server and/or at least onedata carrier, and, secondly, at least one viewing terminal, said datastream enabling the reconstruction of an object associated firstly witha data stream constituted by a set of basic facets and, secondly,coefficients in a base of wavelets corresponding to local modificationsin said basic mesh.

[0070] According to the invention, such a system comprises

[0071] means for the reception of a request defining a portion of saidobject to be displayed;

[0072] means for the analysis of positioning data present in saidstream, as a function of said request, enabling the identification ofthe wavelet coefficients relative to said portion in said data stream;

[0073] means for the extraction of said identified wavelet coefficientsto form a reduced data stream;

[0074] means for the transmission of said reduced data stream.

[0075] The invention also relates to a terminal for the display of anobject associated with a basic mesh constituted by a set of basic facetsand with coefficients in a base of wavelets corresponding to localmodifications in said basic mesh, comprising means for the reception ofa total data stream enabling the reconstruction of said object,furthermore comprising means for the formulation of a request defining aportion of said object to be viewed intended for a server and/or a datacarrier for the reconstruction of said portion from a reduced datastream, comprising wavelet coefficients relative to said portion,received from said server and/or said data carrier.

[0076] A terminal of this kind therefore differs very greatly from theprior art display terminals. Indeed, such a terminal may send a requestto the server, identifying the portion or portions of the meshed objectthat the customer wishes to view and, using only the wavelets associatedwith this portion or portions, that it will have decoded beforehand,reconstruct a representation corresponding to the portion or portions ofthe object. A terminal of this kind therefore differs from the prior artterminals in that it no longer decodes the entirety of a total datastream to be able to select the wavelet coefficients associated with aportion of the object and reconstruct the representation of thisportion.

[0077] The invention also relates to a server comprising means for thestorage of at least one object encoded according to the encoding methoddescribed here above and transmission means implementing thetransmission method described here above.

[0078] The invention finally relates to a device for the encoding of anobject associated with a basic mesh constituted by a set of basicfacets, and with coefficients in a wavelet base corresponding to localmodifications in said basic mesh, said device generating a total datastream enabling the reconstruction of said object, partitioning saidwavelet coefficients into at least two separated subsets, and applyingan independent encoding to each of said subsets, and comprising meansfor the insertion, in said total data stream, of positioning dataenabling the identification of the wavelet coefficients relative to aportion of said objects in said total data stream, so as to enable aselective reconstruction of said portion by means of coefficients of atleast one of said subsets.

[0079] Other features and advantages of the invention shall appear moreclearly from the following description of a preferred embodiment, givenby way of a simple non-restrictive illustration and from the appendeddrawings, of which:

[0080]FIG. 1 is a block diagram of the different steps implementedduring the encoding of a meshed object with at least two dimensionsaccording to the invention;

[0081]FIG. 2 illustrates an exemplary structure of the data streamgenerated during the encoding presented in FIG. 1, and comprisingpositioning data according to a first variant of the invention;

[0082]FIG. 3 provides a detailed view of the structure of the datastream of FIG. 2 when the positioning data indicate a distance withinthe stream;

[0083]FIG. 4 describes an exemplary structure of a data stream generatedduring the encoding of the meshed object with at least two dimensions,comprising positioning data distributed within the stream according to asecond variant of the invention;

[0084]FIG. 5 is a block diagram of the different steps implemented bythe transmission server of the data stream of the FIGS. 2 to 4, uponreception of a request from a customer terminal.

[0085] The general principle of the invention is based on the insertionof positioning data within a data stream generated during the waveletencoding of a meshed object with at least two dimensions, so as toenable a selection and a selective transmission of the coefficients as afunction of the zone of the object with which they are associated.

[0086] Referring now, to FIG. 1, a particular embodiment of the encodingmethod of the invention is presented.

[0087] Here we shall consider the case of an object with at least twodimensions encoded according to a method known as the “wavelet” method.It may be recalled that, according to such a method, the object has,associated with it, a basic mesh and a plurality of wavelet coefficientscorresponding to the refinements to be made to the basic mesh toreconstruct a representation of the object. Each node of the basic meshis therefore associated with a wavelet coefficient.

[0088] It is assumed that the steps of constructing the basic mesh anddetermining the associated wavelet coefficients have already beenimplemented by the encoding device which therefore has available a listof wavelet coefficients associated with the object to be encoded. It maybe recalled that the wavelet coefficient is a triplet of real numbers(x, y, z), accompanied by a piece of information on spatial andfrequency positioning I by which it is possible to know which wavelet acoefficient is associated with. This information I may be, for example,a quadruplet (F0, a, b, c), where F0 represents a facet of the basicmesh, and (a, b, c) represents barycentric coordinates on the face.

[0089] During a step referenced 20, the encoding device partitions allthe wavelet coefficients associated with the meshed object to be encodedinto subsets M₁, M₂, . . . , M_(N). These subsets-are preferablyseparated. They may be constructed, for example, as a function of visualcriteria. Each of them has wavelet coefficients enabling thereconstruction of a representation of a portion of the meshed object tobe encoded.

[0090] For example, if the meshed object to be encoded is a human orsimilar character in three dimensions, it is possible to envisagepartitioning the list of wavelet coefficients into five subsetscorresponding respectively to the subject's face, limbs and bust.

[0091] During a step referenced 21, on each subset M_(i), the encodingdevice defines an arbitrary hierarchy in determining links of parenthoodbetween the different vertices of the subsets as the case may be.Naturally, there is not necessarily any relationship of parenthoodbetween the two vertices of a same subset which may be sibling vertices.

[0092] The encoding device then performs (22) an independent encoding ofthe wavelet coefficients of each of the subsets M_(i), for i varyingfrom 1 to N.Such an encoding is, for example, a “zero-tree” typeencoding, and enables the compression of the representation of thewavelet coefficients, and therefore of the associated mesh nodes, ofeach of the subsets M.

[0093] During a step referenced 23, the encoding device generates atotal data stream comprising, firstly, the result of the encoding (forexample of the “zero-tree” type) of each of the subsets M_(i), and,secondly, positioning data to determine the position of each of thesubsets M_(i) in the stream.

[0094] The structure of such a stream gives greater flexibility in thesending of one or more subsets M_(i) to a display terminal as a functionof a request from a customer.

[0095] Referring to FIG. 2, we now present an embodiment of a datastream 1, generated according to the method of FIG. 1.

[0096] For simplicity's sake, here below in the document, thedescription is limited to the case where each of the subsets M_(i)comprises the wavelet coefficients associated with a basic facet of theobject. It will of course be easy for those skilled in the art togeneralize the following description to the case where a subset M_(i)comprises wavelet coefficients associated with a plurality of basicfacets, or a plurality of nodes of the basic mesh.

[0097] It is assumed here and throughout the rest of the document thatthe facets of the basic mesh are arranged in rising order. For example,an initial facet is arbitrarily selected, and an order of going throughall the basic facets (for example in the trigonometric oranti-trigonometric direction) is selected, so that the initial facet isconsidered to be the first facet, and so on and so forth up to the lastfacet of the basic mesh scanned in the order of scanning, which becomesthe M^(th) basic facet.

[0098] According to the invention, a data stream 1 is generated by theencoding device during the wavelet encoding of an object, for example a3D object. In one particular embodiment of the invention, the datastream 1 comprises a header 10, and a zone of wavelet coefficients 11.

[0099] The zone of wavelet coefficients 11 is preferably divided into aplurality of sub-zones (not shown in FIG. 1,), each grouping the waveletcoefficients associated with a facet of the basic mesh of the object. Asrecalled here above, a wavelet coefficients is a triplet of real numbers(x, y, z), accompanied by a piece of information I on spatial andfrequency position, by which it is possible to know the wavelet withwhich a coefficient is- associated. This piece of information I may be,for example, a quadruplet (F0, a, b, c) where F0 represents the facet ofthe basic mesh, and (a, b, c) represents barycentric coordinates on thisface.

[0100] In a preferred embodiment of the invention, each sub-zonecomprises the “zero-tree” encoding of the wavelet coefficientsassociated with a basic facet. Thus a partitioning of the waveletcoefficients is made along the facet F0 with which they are associated,and as many “zero-tree” encoding operations are performed as there arepartitions. (It may be recalled that, in another embodiment of theinvention described with reference to FIG. 1, the coefficients arepartitioned into a plurality of subsets M_(i), where one and the samesubset can group together several basic facets F0, and an independent“zero-tree” encoding is performed on each of the subsets M_(i). Eachsubset then comprises the “zero-tree” encoding of the waveletcoefficients associated with a subset M_(i)). It is of course alsopossible to envisage the use of any other encoding technique providingfor, satisfactory compression and transmission of the waveletcoefficients. The encoding technique used will preferably be a techniquethat enables a specific encoding of the non-significant parts of theobject considered.

[0101] The header 10 comprises positioning data used to identify each ofthe sub-zones within the zone of wavelet coefficients 11. It furthermorecomprises information on the type of encoding implemented, such asinformation on the type of wavelet functions used, the number of waveletcoefficients, the characteristics of the basic mesh (the number of basicfacets, etc), or again the maximum level of subdivision of the basicmesh.

[0102] In the particular exemplary embodiment presented with referenceto FIG. 3, the zone of the wavelet coefficients 11 is divided into aplurality of sub-zones referenced 111 to 113. Thus the sub-zonereferenced 111 is the “sub-zone 1” associated with the first facet ofthe basic mesh, the sub-zone referenced 112 is associated with thesecond basic facet, and the sub-zone referenced 113 is associated withthe M^(th) basic facet. It will be noted of course that for the sake ofthe simplicity of the figure, not all the sub-zones have been shown.

[0103] The header 10 has a preamble 101, and a plurality of positioningdata referenced 102 to 104. The preamble 101 comprises, for example,data on the type of mesh and the type of wavelets used, mentioned hereabove.

[0104] The zone referenced 102, called “shift 1”, provides informationon the position of the wavelet coefficients associated with the firstbasic facet in the binary stream 1, i.e. it provides information forexample on the distance between the end of the preamble 101 and thestarting point of the “sub-zone 1” referenced 111.

[0105] In a particular embodiment of the invention, such a distance isexpressed in numbers of bits. In another embodiment of the invention,the positioning data zone referenced 102 may of course also provideinformation on the distance between the starting point of the “sub-zone1” referenced 111 and any other reference element of data stream 1, soas to enable the positioning of the wavelet coefficients of the“sub-zone 1” 111 in the bit stream 1.

[0106] In FIG. 3, the “shift 2” zone 103 (and the “shift M” zone 104respectively) provide information on the number of bits between thestarting point of the “sub-zone 2” 112 (and the “sub-zone M” 113respectively) and the end of the preamble 101.

[0107] Thus, when a server, in response to a request from a customerterminal, wishes to send this terminal the wavelet coefficientsassociated with the M^(th) basic facet, it consults the 'shift M”positioning data 104 of the header 10. The “shift M” zone 104 informsthe server of the number of bits between the end of the preamble 101 andthe starting point of the “sub-zone M” 113, and the server can thereforetake position directly at the starting point of the “sub-zone M” 113, soas to extract and then transmit these coefficients alone to the customerterminal.

[0108] The data stream 1 of FIG. 4 comprises a header 10 and a zone ofwavelet coefficients 11, comprising firstly sub-zones of waveletcoefficients referenced 111 to 113 and zones of positioning datareferenced 120 to 123. In such an alternative embodiment, thepositioning data referenced 120 to 123 are therefore distributed in thedata stream 1, and not assembled in the header 10 as above.

[0109] The positioning data 120 to 123 are, for example, markersindicating the starting point and/or the end of the sub-zone of waveletcoefficients. Thus, the zone “mark 1” referenced 120 indicates thestarting point of the “sub-zone 1” 111, comprising the waveletcoefficients associated with the first facet of the basic mesh. The zone“mark 2” referenced 121 marks the starting point of the“sub-zone 2”referenced 112, and the zone “mark M” referenced 123 marks the startingpoint of the “sub-zone M” referenced 113.

[0110] In one particular embodiment of the invention, the informationcontained in the zones “mark 1” 120, “mark 2” 121 and so on and so forthuntil “mark M” 123 are identical. In other words, a plurality ofidentical markers is inserted in the zone of wavelet coefficients 11 ofthe data stream 1 so as to separate the different sub-zones eachassociated with a facet of the basic mesh. Thus, when a server wishes tosend the wavelet coefficients associated with the “sub-zone M” 113 to adisplay terminal, it scans the entire stream 1 and counts the markersthat it has encountered so as to determine which is the M^(th) marker123, and also determine the starting point of the “sub-zone M” 113,comprising the “zero-tree” encoding of the wavelet coefficientsassociated with the M^(th) basic facet. Thus, the customer terminalreceives only the wavelet coefficients of the “sub-zone M” 113, and doesnot need to decode the entire stream 1 to access the waveletcoefficients that it needs.

[0111] In another embodiment of the invention, the markers referenced120 to 123 are specific to a given sub-zone of the zone of waveletcoefficients 11. The marker “mark 1” 120 specifically indicates thestarting point of the “sub-zone 1” 111, the marker “mark 2” 121specifically indicates the starting point of the “sub-zone 2” 112, andso on and so forth. (It is of course possible to envisage, for example,a situation where the markers referenced 120 to 123 indicate the end ofthe associated sub-zones 111 to 113.)

[0112] Thus, a server wishing to transmit the coefficients of the“sub-zone M” 113 in response to a request from a customer goes throughthe data stream 1, until it identifies the marker “mark M” 123, anddeduces the position of the starting point of the “sub-zone M” 113therefrom .

[0113] It is again possible to envisage any other embodiment of theinvention that is not shown in FIGS. 3 and 4 but enables theconstruction of a data stream 1, in which there are inserted positioningdata enabling a server to determine the position of a sub-zone ofwavelet coefficients associated with a basic facet, or more generallywith the sub-set M_(i) grouping together a plurality of nodes or basicfacets, with a view to its extraction and selective transmission inresponse to a request from a customer.

[0114] For example, it is possible to envisage an embodiment combiningthe alternative embodiments of the invention shown with reference toFIGS. 3 and 4, in which the sub-zone referenced 111 to 113 would begrouped together in sets of three or four sub-zones. Positioning data,inserted in the header 10, would provide information on the distancebetween a referenced element (for example the end of the preamble 101)and the starting point of a set of sub-zones. Markers would be insertedin a set of this kind, so as to indicate the starting point and/or theend of each of the sub-zones of the entire unit.

[0115] Thus, through the positioning data located in the header 10, aserver can get positioned directly at the starting point of the set ofsub-zones, and then scan the set and, through the markers, determine theposition of the sub-zone or sub-zones of the set that it must transmitin response to a request from a customer.

[0116] Here below, referring to FIG. 5, we shall present the differentsteps implemented by a server, or by a terminal that is connected to adata carrier and is responsible for transmitting the associated waveletcoefficients to a zone of the basic mesh, in response to a request froma customer. For simplicity's sake, the description shall be limited herebelow to processing operations implemented by a server in response to arequest from a display terminal. Those skilled in the art will easilydeduce the processing operations to be performed when the object datacome from a data carrier connected directly or indirectly to the displayterminal.

[0117] It is assumed that the customer wishes to look at a detail of thescene that he is viewing on his terminal. The terminal therefore sendsthe server a request specifying the portion of the scene for which hewishes to obtain the wavelet coefficients determining the refinements tobe made in the basic mesh to obtain a satisfactory reconstruction of theportion.

[0118] During a step referenced 40, the server receives the request fromthe customer terminal, and determines the facets of the basic meshconcerned by the request. During a step referenced 41, the server scansthe data-stream generated at output of a device for encoding the scene,and analyses the positioning data present in this stream. For example,it consults the positioning data contained in the header of the stream.

[0119] During a step referenced 42, it determines the position of thesub-zones of wavelet coefficients associated with the portion of thescene considered, as a function of the positioning data that it hasanalyzed earlier. After identification (42) of the wavelet coefficientspertaining to the object portion to be viewed, the server extracts (43)these coefficients from the total data stream so as to form a reducedstream intended for the customer terminal.

[0120] During a step referenced 44, the server sends this reduced streamto the customer's display terminal, so that the terminal can reconstructthe portion of the scene that the customer wishes to view, withouthaving to decode the entire total data stream.

1. A method for the encoding of an object with at least two dimensions,that is associated with a basic mesh consisting of a set of basicfacets, and with coefficients in a base of wavelets corresponding tolocal modifications in the basic mesh, the method delivering a totaldata stream that can be used to reconstruct the object, characterized inthat the wavelet coefficients are partitioned into at least twoseparated subsets each undergoing an independent encoding, andpositioning data are inserted in the total data stream, enabling theidentification of wavelet coefficients relative to a portion of theobject in the total data stream, so as to enable a selectivereconstruction of the portion by the coefficients of at least one of thesubsets.
 2. The method according to claim 1, characterized in that eachof the separated subsets is a basic facet.
 3. Method according to claim1, characterized in that the encoding implements the following steps:the detection of at least one non-significant part; the specificprocessing of each of the non-significant parts.
 4. The method accordingto claim 1, characterized in that the encoding implements a “zero-tree”type of technique.
 5. The method according to claim 1, characterized inthat the total data stream comprises a header, comprising at leastcertain of the positioning data, and a wavelet coefficient zone,comprising a sub-zone identified by the positioning data for each of theseparated subsets.
 6. The method according to claim 5, characterized inthat the positioning data contained in the header identify a sub-zone,in defining a distance between the position of an identified element anda starting point of the sub-zone in the stream.
 7. The method accordingto claim 5, characterized in that the header further comprises at leastsome pieces of the information belonging to the group comprising: thenumber of basic facets; the type of wavelets; information concerning theobject; information concerning the encoding of the positioning data. 8.The method according to claim 1, characterized in that the total datastream comprises at least one zone of wavelet coefficients, comprising asub-zone identified by the positioning data for each of the separatedsubsets, the positioning data comprising at least one marker at astarting point and/or at an end of each of the sub-zones.
 9. The methodaccording to claim 5, characterized in that the sub-zones are organizedin the stream by rising order of basic facet.
 10. A method for thetransmission of a data stream between, firstly, at least one serverand/or at least one data carrier and, secondly, at least one displayterminal, the data stream enabling the reconstruction of an objectassociated firstly with a basic mesh constituted by a set of basicfacets and, secondly, coefficients in a wavelet base corresponding tolocal modifications in the basic mesh, the method being characterizedby: a step for the reception of a request defining a portion of theobject to be viewed; a step for the analysis of positioning data presentin the stream, as a function of the request, allowing identify ofwavelet coefficients relative to the portion in the data stream; a stepfor the extraction of the identified wavelet coefficients to form areduced data stream; a step for the transmission of the reduced datastream.
 11. A signal representing an object associated with a basic meshconsisting of a set of basic facets, and with coefficients in a base ofwavelets corresponding to local modifications of the basic mesh,characterized by at least one zone of wavelet coefficients and at leastone positioning zone, comprising positioning data enabling theidentification of the wavelet coefficients pertaining to a portion ofthe object in the signal.
 12. The signal according to claim 11,characterized in that, the wavelet coefficients are partitioned into atleast two separated subsets, each undergoing an independent encodingoperation, the signal comprises a header comprising at least some of thepositioning data, and a zone of wavelet coefficients, comprising asub-zone identified by the positioning data for each of the subsets. 13.The signal according to claim 11, characterized in that, the waveletcoefficients are partitioned into at least two separated subsets eachundergoing an independent encoding, the signal comprises at least onezone of wavelet coefficients, comprising a sub-zone identified by thepositioning data for each of the subsets, the positioning datacomprising at least one marker at a starting point and/or at an end ofeach of the sub-zones.
 14. A total data stream recorded on a carrierusable in a computer and enabling the reconstruction of an encodedobject with at least two dimensions, that is associated with a basicmesh constituted by a set of basic facets, and with coefficients in abase of wavelets corresponding to local modifications in the basic mesh,characterized in that the wavelet coefficients are partitioned into atleast two separated subsets each undergoing an independent encoding, andin that, in the total data stream, there are inserted positioning dataenabling the identification of the wavelet coefficients relative to aportion of the object in the total data stream, so as to enable aselective reconstruction of the portion by the coefficients of at leastone of the subsets.
 15. The data stream according to claim 14,characterized in that it enables the reconstruction of an object with atleast two dimensions encoded with a basic mesh consisting of a set ofbasic facets, and with coefficients in a base of wavelets correspondingto local modifications in the basic mesh, characterized in that thewavelet coefficients are partitioned into at least two separated subsetseach undergoing an independent encoding, and positioning data areinserted in the total data stream, enabling the identification ofwavelet coefficients relative to a portion of the object in the totaldata stream.
 16. A system for the transmission of a data stream between,firstly, at least one server and/or at least one data carrier, and,secondly, at least one viewing terminal, the data stream enabling thereconstruction of an object associated firstly with a data streamconstituted by a set of basic facets and, secondly, coefficients in abase of wavelets corresponding to local modifications in the basic mesh,characterized in that the system comprises: means for the reception of arequest defining a portion of the object to be displayed; means for theanalysis of positioning data present in the stream, as a function of therequest, enabling the identification of the wavelet coefficientsrelative to the portion in the data stream; means for the extraction ofthe identified wavelet coefficients to form a reduced data stream; meansfor the transmission of the reduced data stream.
 17. A terminal for thedisplay of an object associated with a basic mesh constituted by a setof basic facets and with coefficients in a base of waveletscorresponding to local modifications of the basic mesh, comprising meansfor the reception of a total data stream enabling the reconstruction ofthe object, characterized in that it further comprises means for theformulation of a request defining a portion of the object to be viewedintended for a server and/or a data carrier for the reconstruction ofthe portion from a reduced data stream, comprising wavelet coefficientsrelative to the portion, received from the server and/or the datacarrier.
 18. A server comprising means for the storage of at least oneobject encoded according to the method of claim
 1. 19. A device for theencoding of an object with at least two dimensions associated with abasic mesh constituted by a set of basic facets, and with coefficientsin a wavelet base corresponding to local modifications in the basicmesh, the device generating a total data stream enabling thereconstruction of the object, characterized in that the devicepartitions the wavelet coefficients into at least two separated subsets,and in that the device applies an independent encoding to each of thesubsets, and in that the comprises means for the insertion, in the totaldata stream, of positioning data enabling the identification of thewavelet coefficients relative to a portion of the objects in the totaldata stream, so as to enable a selective reconstruction of the portionby the coefficients of at least one of the subsets.
 20. The server ofclaim 18 further comprising transmission means for transmitting a datastream enabling the reconstruction of an object associated firstly witha basic mesh constituted by a set of basic facets and, secondly,coefficients in a wavelet base corresponding to local modifications inthe basic mesh, the transmission means being characterized by: means forthe reception of a request defining a portion of the object to beviewed; means for the analysis of positioning data present in thestream, as a function of the request, allowing identify of waveletcoefficients relative to the portion in the data stream; means for theextraction of the identified wavelet coefficients to form a reduced datastream; means for the transmission of the reduced data stream.